Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/08—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials
  • C09K11/77—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials containing rare earth metals
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/08—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials
  • C09K11/77—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials containing rare earth metals
  • C09K11/7713—Sulfates
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/08—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials
  • C09K11/77—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials containing rare earth metals
  • C09K11/7704—Halogenides
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/2012—Measuring radiation intensity with scintillation detectors using stimulable phosphors, e.g. stimulable phosphor sheets
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens

Definitions

• thermoluminescent phosphor a thermoluminescent phosphor and a process for the preparation thereof.
• Ionizing radiation such as X-rays, alpha rays, beta rays, and gamma rays
• Dosimeters may measure an individual's or an object's radiation dose and also cumulative dose which is accumulated over a period of time.
• a thermoluminescent dosimeter is a type of radiation dosimeter which measures ionizing radiation dose by measuring the amount of visible light emitted from a crystal in the detector when the crystal is heated after its irradiation. The amount of light emitted depends upon the amount of radiation exposure received by it. TLD is extensively used for radiation monitoring of workers engaged in radiation area and environmental radiation measurement.
• CaSO4 Calcium Sulphate
• TLD Thermoluminescent
• Dysprosium (Dy) doping in particularly has been the most successful in the series.
• CaSO ⁇ .Dy is always the choice when it comes to radiation exposures for personnel monitoring. It remains one of the most attractive TLD materials because of ease preparation in large quantity with essentially the same Thermoluminescent (TL) properties and its high sensitivity. The stability of its response even in adverse climatic conditions further adds to its demand in monitoring doses in the field.
• TSL Thermally Stimulated Luminescence
• Literature survey shows that the first synthetic CaSO4, activated with Manganese (Mn), showed high sensitivity, but its glow curve exhibited a single peak at low temperature (90°C). Therefore, fading of radiation dose recorded of this material was very pronounced (40-85% in the first 3 days after exposures) .
• the credit for the development of a highly sensitive CaS04 TLD material goes to Yamashita et al. Later Nambi et al. have studied the TL properties of CaS04 phosphors doped individually by different rare earth (RE) elements and concluded that Dysprosium (Dy) and Thulium (Tm) are the most efficient activators and that the optimum concentration of the dopant is 0.1%.
• thermoluminescent phosphor which is Ultrasensitive compared to known materials.
• thermoluminescent phosphor which is easy to prepare.
• Another object of this invention is to propose a thermoluminescent phosphor, which can measure low radiation doses.
• thermoluminescent phosphor which is cost-effective.
• Fig. 1 Set-up for samples preparations by recrystallisation method.
• Fig. 2 TL glow curves for CaSO4:Dy(x), Mn(l-x) for x varing in steps of 0.025 mol% for a Gamma dose of 1 Gy. The highest TL intensity was found for glow curves for CaSO 4 :Dy (0.025), Mn(0.075).
• TL glow curve (a) represents CaSO4:Dy(0.1mol%)
• curve(b) represents CaSO 4 :Mn(0.1 mol%)
• curve (c) shows CaS0 4 :Dy (0.025 mol%), Mn (0.075mol%) for a Gamma radiation dose of 1 Gy.
• Fig. 4 TL response curves of CaS0 4 :Dy (0.025), Mn (0.075) sample subjected to gamma rays in the dose range of 10 Gy-100Gy (10 micro Gray- 100 Gray)
• Fig. 5 Graphs for fading of microcrystalline CaS0 4 :Dy and CaS0 4 :Dy (0.025), Mn (0.075)
• Fig. 6 A Breast Phantom with TL phosphors pasted on it being irradiated in mammography Unit (a).
• Fig. 7 TL Response for new CaS0 4 :Dy, Mn and CaSO 4 :Dy in mammography.
• the radiation dose was varied by charging x ray tube current (mA) and exposure time(s).
• thermoluminescent phosphor and a process for the preparation thereof.
• the thermoluminescent phosphor is CaS04: Dy,Mn.
• the procedure of preparation of CaSO4 involves the standard production route known which is based on the recrystallization method as proposed by Yamashita et al [T. Yamashita, N. Nada, H. Onishi and S. Kitamura, Calcium sulphate activated by thulium or dysprosium for thermoluminescence dosimetry, Health Phys. 21 ( 1971) 295.].
• Yamashita et al the difference between the method adopted by Yamashita et al. and the process according to the instant invention lies in the activator compounds i.e.
• Dysprosium in the form of DyCb
• DyCb oxide salt of Dysprosium
• MnC Manganese
• the acid vapours are sucked through an air flux created by suction pump, and collected in the flask (5).
• the powder thus obtained in the closed system is the required microcrystalline phosphor of CaSO4:Dy,Mn.
• the sample is washed several times with water to remove any traces of residual acid.
• the optimized concentration of 0.1 mol% of Dy was kept constant for preparation of other samples.
• the CaSO4:Dy in 0.1mol% was prepared so that it may serve as control.
• CaSO4.Mn was prepared by doping host CaSO4 with Manganese (Mn) in the form of MnCb by the same method of preparation keeping the Mn concentration to be 0.1 mol%.
• CaS04:Mn was prepared as control phosphor in order to carry out comparison studies with new phosphor CaS0 4 :Dy,Mn and another control phosphor CaS04:Dy.
• a new TL phosphor CaS04.Dy,Mn was prepared by adding Dy in the form of DyCb and Mn in the form of MnCb into the host compound CaS0 4 .
• the molar concentration of the dopants Dy and Mn were varied and it was that the concentration affects the sensitivity of the phosphor.
• the ratio of Dy and Mn was varied as CaS04:Dy (x),Mn (1-x) where x varies from 0 to 1 in steps of 0.025 mol%, total quantity of dopants being 0.1 mol%.
• Table 1 shows the effect on TL intensity with variation in the dopant concentration of Dy and Mn.
• Another control CaS04:Mn has the peak at low temperature at around 110°C and hence prone to show pronounced fading of TL intensity with time (literature reports 40-85% fading in 3 days).
• the new phosphor CaSO4:Dy,Mn has peak at around 240°C and hence has much low fading of 11% in 3 months.
• the sample CaSO4:Dy(0.025),Mn(0.075) showed a good TL intensity, it was further tested for its dose response with different doses of gamma irradiation.
• the sample was irradiated in a radiation dose range of 10 microGray ⁇ Gy) to 100 Gray (Gy).
• the TL response curves of CaSO4".Dy(0.025),Mn(0.075) samples irradiated by gamma rays are shown in Fig. 4.
• the response curve of the material irradiated by gamma rays with a dose range of 10 ⁇ Gy to 100 Gy shows linearity in the full range.
• the TL fading curve of CaSO 4 :Dy(0.25),Mn(0.75) and the standard (control) phosphor CaS04:Dy was also recorded and is shown in Fig. 5. Both the samples were irradiated with a radiation dose of 1 Gy and stored in a simple vial without taking any precautions to shield it from light and humidity and the glow curves were recorded at various intervals for a period of around 90 days. The variation in the peak intensity over the storage time gives the amount of fading in the sample. Fading of about 10% in CaS0 4 :Dy while the fading in our new phosphor CaSO4:Dy(0.25),Mn(0.75) was observed to be 11%.
• the new thermoluminescence material CaSO4:Dy(0.25), Mn(0.75) is a very sensitive TL material which can measure small radiation accurately since it is about twice sensitive than the CaS04:Dy.
• the new material is also capable of measuring large radiation doses since its response to radiation in linear in a very wide range.
• the new TL material CaS04".Dy, Mn being very sensitive can be used to measure the smaller radiation doses.
• this new TL compound was irradiated along with control; CaS04:Dy in a mammography machine ( Figure 6a) and a radiography machine ( Figure 6b) pasted on human stimulation phantoms.
• Mammography uses low-energy X-rays to image the human breast and is used as a diagnostic and a screening tool for detection of breast cancer tumor.
• the goal of mammography is the early detection of breast cancer typically through detection of characteristic masses and/ or microcalifications.
• Mammograms use low doses of ionizing radiations to create images which are then analyzed by the Radiologists for any abnormal Findings. The examination is performed by selecting parameters such as kVp (peak kilo voltage) and mAs (milli Ampere second) which is applied to x- ray tube for generation of x-rays from x-ray tube. The selection of kVp and mAs determines the energy and quantity of x-ray photons.
• kVp and mAs are selected on the basis of the breast thickness and density of the patient.
• CaSO4:Dy(0.25),Mn(0.75) and the standard (control) sample CaS04:Dy were irradiated with 23 kVp x-rays with mAs varying in the range of 10 to 500 by a mammography X-ray unit manufactured by Philips Mammo Dignost using a breast simulator called mammography phantom.
• the radiation doses were varied by controlling the imaging machine parameters to obtain full range of radiation doses.
• This new TL material (phosphor) CaSO4:Dy(0.25),Mn(0.75) which has optimised Dy and Mn ratio exhibits improved TL properties and an increased TL intensity by a factor of approximately two over the existing standard CaS04:Dy and overcomes the major disadvantage of high fading of CaS04:Mn (due to low temperature peak of CaSO4:Mn).
• the standard (control) microcrystalline CaS04.Dy phosphor (better known as TLD 900) is a sensitive phosphor but the sensitivity of the phosphor CaSO4:Dy(0.25),Mn(0.75) according to the invention is even better.
• Most of the phosphors known today show sublinear response at low doses and this poses a problem in estimating the low radiation doses. Since radiation doses in any amount entails certain risk, its dosimetry is important.
• CaSO4:Dy(0.25),Mn(0.75) material could be a good candidate for low doses as it has a good sensitivity at low doses and is linear to a wide range of radiation exposures. Also, the fading of CaSO4:Dy(0.25),Mn(0.75) is similar to that of CaSO4:Dy estimated over a period of three months. All these confirm that the new phosphor CaSO 4 :Dy(0.25),Mn(0.75) is more suitable for radiation dosimetry than standard CaSO4:Dy material.

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• 2015
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